ANISOTROPIC VORTEX LATTICE IN YBA2CU3O7

Abstract

We report on small angle neutron scattering observations of the flux line lattice (FLL) in a single crystal of YBa2Cu3O7. To probe the mass anisotropy ratio, m3/m1, measurements were made as a function of angle, THETA, between the 8 kOe applied field and the crystallographic (001) axis for 0-degrees less-than-or-equal-to THETA less-than-or-equal-to 80-degrees. With the rotation about an a/b (or y) axis, two symmetry-related distorted hexagonal FLL domains formed. Contrary to theoretical prediction, the lattices formed are consistent with a rotation of the short basis vector, a1, from the x axis by 15-degrees, after the effects of anisotropy are removed. The mass ratio is 20 +/- 2, which is slightly lower than published values. The temperature dependence of the intensity is not conventional.